1. Field of the Invention
This invention relates to a method for producing a unidirectionally solidified casting and an apparatus for producing the same, and, more particularly, to a directional solidification casting method for casting a stationary blade, a rotor blade or the like such as that of a gas turbine, and an apparatus for casting the same.
2. Description of the Related Art
Conventionally, a Bridgeman method has been used to produce a casting that has a part onto which a great thermal and mechanical load is imposed. A stationary blade or a rotor blade of a gas turbine formed intricately can be mentioned as one example of such a part. A casting directionally solidified according to the Bridgeman method exhibits single crystals or columnar crystals oriented in advantageous directions.
A description will be given of a conventional method for producing a directionally solidified casting with reference to FIG. 8. A directionally solidified casting has been conventionally produced such that, as shown in FIG. 8, a driving rod 42 is lowered in the direction of an arrow along axial line A—A, and a mold 20 placed on a cooling plate 41 is drawn out from a heating chamber 10. When molten metal 32 in the mold 20 passes through a water-cooled ring 51, the metal 32 is cooled by radiational cooling, etc., and is solidified into a casting 31. Instead of the method using the water-cooled ring 51 shown in the figure, another cooling method has also been employed in which cooling gas is jetted onto the mold 20.
Still another cooling method, such as a cooling bath method or a method in which the mold 20 is placed into a heat conduction pipe, has been employed.
Art disclosed in Japanese Patent Provisional Publication Nos. 9-10919/1997 and 9-206918/1997, etc., is known as the directional solidification casting method and apparatus described above.